A wide-angle lens may be used in various applications including cameras installed in vehicles and security cameras, for example. With respect to an image capturing lens of a camera installed in a vehicle, techniques for capturing a clear image with a wide angular range are in demand. Additionally, there is a growing demand for a technique for enabling simultaneous capture of a wider angular range of view exceeding 180 degrees in the left and right directions.
One advantage of securing an angular range of view exceeding 180 degrees in the left and right directions with an image capturing lens of a camera installed a vehicle is that image information of the surrounding view of the vehicle in all directions, namely, front, back, left, and right directions, may be captured, free of dead angles, by arranging one image capturing lens at each of four sides of the vehicle, for example.
It is noted that an apparatus for capturing the surrounding image of a vehicle is disclosed in Japanese Laid-Open Patent Publication No. 2006-224927, for example.
Also, a fish-eye type wide-angle image capturing lens including four lenses that can secure a view of at least 180 degrees in the left and right directions is disclosed in Japanese Laid-Open Patent Publication No. 2005-227426, for example.
According to the above disclosure, aspheric surface lenses made of plastic material is used and the number of lenses making up the image capturing lens is reduced to four lenses in an attempt to achieve miniaturization and weight reduction. However, there are limits to achieving cost reduction and miniaturization using the above-disclosed technique because the object side lens (first lens) of the disclosed lens structure has a relatively large radius. Also, because plastic that may be used as lens material has a limited refractive index/Abbe number range, chromatic aberration of magnification may not be adequately corrected and color fringing may easily occur. Thus, the lens thickness may not be adequately reduced which in turn becomes an obstacle to reducing the size of the image capturing lens. Further, because a relatively large number of lenses with aspheric surfaces are used, image degradation may occur due to assembling errors in the manufacturing process or changes in the usage environment such as the temperature.